Luminescent display tube anode assembly comprising anode structures having channel-shaped conductive layers

ABSTRACT

An anode assembly for a luminescent display tube includes a substrate having a number of recesses of predetermined configuration formed in one major surface. An anode structure is formed in each of these recesses so that the anode structure conforms substantially to the shape of the recess. Each anode structure includes a layer of conductive material disposed on the bottom surface of the recess and projecting members or ridges of conductive material which are contiguous with the layer of conductive material and extend upward along the opposed side surfaces of the recess. When the anode structure is formed in an elongated recess, a channel shaped conductive layer results which is made up of the conductive layer on the bottom of the recess and the projecting members extending along the opposed sides of the recess.

United States Patent [191 Akahane et al.

[451 Feb. 4, 1975 [75] Inventors: Fumitake Akahane; Masaki Kobayakawa; Kazufumi Yawata, all I of Kagoshima, Japan [73] Assignee: Nippon Electric Kagoshima,

Limited, Kagoshima, Japan 22 Filed: May8, 1974 211 App]. No.: 468,294

[30] Foreign Application Priority Data UNITED STATES PATENTS 4/1970 Tanji 313/497 3,619,694 11/1971 Tanji 313/497 3,737,705 6/1973 Takeda et al7 313/496 Primary Examiner-Palmer C. Demeo Attorney, Agent, or Firm-Hopgood, Calimafde, Kalil, Blaustein & Lieberman [57] ABSTRACT An anode assembly for a luminescent display tube includes a substrate having a number of recesses of predetermined configuration formed in one major surface. An anode structure is formed in each of these recesses so that the anode structure conforms substantially to the shape of the recess. Each anode structure includes a layer of conductive material disposed on the bottom surface of the recess and projecting members or ridges of conductive material which are contiguous with the layer of conductive material and extend upward along the opposed side surfaces of the recess. When the anode structure is formed in an elongated recess, a channel shaped conductive layer results which is made up of the conductive layer on the bottom of the recess and the projecting members extending along the opposed sides of the recess.

9 Claims, 5 Drawing Figures PATENTED FEB 4 I975 SHEET 2 OF 2 1 LUMINESCENT DISPLAY TUBE ANODE ASSEMBLY COMPRISING ANODE STRUCTURES HAVING CI-IANNEDSI'IAPED CONDUCTIVE LAYERS BACKGROUND OF THE INVENTION This invention relates generally to a luminescent display tube and particularly to an anode assembly for such a display tube.

As described in U.S. Pat. Nos. 3,508,103 and 3,619,694, a luminescent display tube includes an evacuated sealed envelope, having an anode assembly mounted within the envelope. The anode assembly includesa substrate which is formed of an insulating'material and is provided with a plurality of luminescent anode structures. A cathode is arranged in front of the anode structures for emitting thermal electrons and a grid is disposed between the anode structures and the cathode. A voltage supply for supplying predetermined electric voltages is connected between the cathode and grid and between the cathode and a selected one of the anode structures to provide a substantially uniform distribution of electrons on the selected anode structure to render the structure luminescent. Operating voltages for a number of anode structures may be simultaneously applied between the cathode and selected ones of the anode structures to make all these selected anode structures luminesce together.

To provide the anode structures a plurality of recesses, many of which are elongated, are formed in the substrate in the geometric configuration required to provide the numerals or other symbols to be selectively displayed. Each anode structure comprises a layer of an electroconductive material which is disposed on the bottom surface of the recess in electrical contact with the anode structure voltage supply means. A layer of a luminescent material is then provided over the electroconductive material layer and on the sides of the recess.

With a conventional tube of the type described above, it has been found that luminescence is emitted only from the planar surface area of the luminescent material layer which is substantially that portion over the electroconductive layer. The brightness of the display is determined consequently by the brightness of wherein the luminescent layers of the anode structure the planar surface of the luminescent material. In addition, the luminescent material layers will often come loose from the supporting substrate in anode structures of this prior art type.

It is therefore an object of the present invention to provide an anode assembly for a luminescent display tube, which will have a brighter display than the conventional anode assembly of a luminescent display tube.

It is another object of this invention to provide an anode assembly for a luminescent display tube, which will generate about twice as bright a display as that generated by a conventional anode assembly of a luminescent display tube.

It is still another object of this invention to provide an anode assembly for a luminescent display tube in which a larger surface area of each anode structure of the anode assembly luminesces.

It is an additional object of this invention to provide an anode assembly for a luminescent display tube,

are less likely to peel off the substrate.

SUMMARY OF THE INVENTION An anode assembly for a luminescent display tube includes a substrate having a plurality of recesses formed in one surface. A plurality of anode structures are provided, and each of the anode structures is disposed within one of the recesses in the substrate. Each of the anode structures includes a layer of electrically conductive material disposed on the bottom surface of the I recess and at least one projecting member which is composed of electrically conducting material and is contiguous with the electrically conductive layer. This projecting member extends outwardly from the electrically conducting layer into the recess. A layer of a luminescent material covers the electrically conducting layer and the projecting member.

Preferably, one projecting member is in contact with at least one side surface of the recess. A second projecting member may be provided in contact with the side surface of the recess which is opposite to the side surface contracted by the first projecting member. In addition, each anode structure may further include an additional similar projecting member or members, one of which is preferably substantially equally spaced from the opposing side surfaces of the recess. These projecting members will provide an enlarged surface area for the luminescent material layer and will tend to prevent the luminescent material layer from peeling off the substrate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view ofa portion of the anode assembly for a luminescent display tube.

FIG. 2 is a cross-sectional view of a conventional anode assembly, taken along the plane AA of FIG. 1.

FIG. 3 is a cross sectional view of a first embodiment of the anode assembly of the present invention, taken on line AA of FIG. 1.

FIG. 4 is a cross sectional view of a second embodiment of the anode assembly of the present invention, taken along plane AA of FIG. 1.

FIG. 5 is a cross sectional view of a third embodiment of the anode assembly of the present invention, taken along the plane A-A of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, a conventional anode assembly for a luminescent display tube will be described at first in order to facilitate understanding of the present invention. The anode assembly comprises a substrate ll of an insulating material on which a set of anode structures 12 is disposed. In the example being illustrated, seven anode structures a, b, c, d, e,f, and g are arranged substantially in a figure eight so that they can be activated to display any one of the numerals 0 through 9. An additional anode segment h serves to display the numeral 4 in a more agreeable shape. A further segment DP, used to indicate a decimal point, is also depicted. Two of these anode structures e and c are shown in cross section in FIG. 2. As can be seen in FIG. 2, the substrate 11 comprises a first base plate 21 having holes 15 formed therethrough in conformity with the desired geometric configuration of the anode segments 12 shown in FIG. 1. A second base plate 22 has a plurality of electroconductive layers 23 formed on one of its surfaces. The electroconductive layers 23 are made to be wider than the cross-sectional areas of the respective holes that they are beneath. Each of the electroconductive layers 23 has a lead wire portion 24 which extends from the layer 23 through the second base plate 22 to the opposite surface of the second base plate 22. The substrate 11 also includes a third base plate 26 on which a plurality of leads 27 are formed. The leads 27 are electrically connected with the respective lead wire portions 24. The anode structures 12 include the electroconductive layers 23 and a layer 29 of a luminescent material which covers each of the electroconductive layers 23. The base plates 21, 22, and 26 may, for example, be made of glass or a ceramic material. The electroconductive layers 23 and the lead wire portions 24 may be formed by metallizing or printing. The leads 27 may also be formed by metallizing or printing. If desired, the base plates 21, 22, and 26, the electroconductive layers 23, and the leads 27 may be formed by screen printing a metal paste on green tapes and co-firing the paste and the tapes to form an integral substrate 11 having the conductive portions 23, 24, and 27. In the completed anode assembly, the holes 15 formed through the first base plate 21 become grooves or recesses conforming in geometrical configuration to the anode structures 12, as shown, for instance, in the arrangement of FIG. 1. The luminescent material layers 29 may be formed by depositing the luminescent material in the respective holes 15 or by subjecting the luminescent material to electrodeposition. It will be noted that the exposed surface of each luminescent material layer 29 is recessed to provide an inwardly directed area 30 which is coextensive with the side or peripheral surface of the hole 15.

In operation, an electric field is applied perpendicularly to the electroconductive layer 23. A voltage is applied to layer 23 through lead 27 to cause thermal electrons accelerated by the electric field to impinge on the luminescent material layer 29 which covers the electroconductive layer 23. It has now been confirmed that the inwardly directed area 30 of the luminescent material layer 29 does not contribute materially to the brightness ofthe anode structure. In addition, the luminescent material layer 29, particularly if it is a wide one, often tends to become loosened from the underlying electroconductive layer 23 and falls off the anode structure.

Referring now to FIGS. 1 and 3, a first embodiment of the present invention will be described. The first embodiment of the invention as shown in FIG. 3 includes in addition to the elements described in connection with FIG. 2 a projecting member 31 formed of an electroconductive material integrally with each of the electroconductive layers 23. Preferably, the material of which each of the projecting members 31 is composed is the same as the material of the electroconductive layers 23. The projecting members 31 are in contact with the peripheral surface of each of the recesses 15 and are arranged so that they underlie the inwardly directed area 30 of the associated luminescent material layer 29. If the recesses are elongated, such as e and c of FIG. 1, the projecting members 31 are preferably arrangedin contact with substantially the whole area of the two lateral opposed sides of the recess.

It has become possible with this arrangement to make the inwardly directed areas 30 of the luminescent layer 29 contribute to the brightness of the display. If an anode structure is formed in a groove or recesses 15 which is 500 microns wide and 300 microns deep, it has been found that the brightness will be increased by about percent by utilizing this invention.

Referring to FIGS. 1 and 4, a second embodiment of this invention is shown which includes a projecting member 32 in addition to members 31. This additional projecting member 32 is formed of the same electroconductive material as the electroconductive layers 23. Projecting members 32 are integral with the respective electroconductive layers 23. The projecting member 32 is preferably substantially equally spaced from the opposed peripheral surfaces of the hole or recess 15 involved. In the embodiment of FIG. 4 the luminescent material layer 29 covers both the projecting members 31 and 32.

By using the additional projecting members 32, it is possible to further enlarge the surface area of the luminescent matrial layer 29 and to accordingly increase the brightness of the display. In addition, the second projecting member 32 serves to prevent the overlying luminescent material layer 29 from coming off the underlying electroconductive layer 23.

Referring to FIGS. 1 and 5, a third embodiment of this invention includes only a single projecting member 33 formed of the same electroconductive material as the electroconductive layers 23. The projecting member 33 is integral with each of the electroconductive layers 23. Preferably, the projecting member 33 is substantially equally spaced from the sides or peripheral surfaces of the hole or recess concerned.

Although it is impossible with this third embodiment to make the inwardly directed area 30 of luminescent material layer 29 contribute to the brightness of the display, the luminescent material layer 29 overlying the projecting member 33 according to this embodiment will enhance the brightness of the anode structure. In addition, the projecting member 33 will aid in preventing the luminescent material layer 29 from peeling off of the underlying electroconductive material layer 23.

It will now be appreciated that a plurality of projecting members may be formed integrally with the electroconductive layer 23 in each of the holes or recesses 15. As indicated above, two of these projecting members can be arranged along the opposed sides of the recesses involved. Other projecting members may be placed between the opposing side surfaces of the recess, either equally or unequally spaced from the side surfaces. The projecting member 31, shown in FIGS. 3 and 4, should preferably be in contact with substantially the whole areas of the opposing side surfaces of an elongated recess 15, although if desired the protrusion 31 may be in contact with only one of the side surfaces of the recess 15. In other words, it is preferable that the electroconductive layer 23 and the associated projecting members 31 should form a channel-shaped conductive layer when the recess 15 is of an elongated shape. It is to be noted that the projecting members need not be as uniform in structure as the planar electroconductive layers 23. This fact facilitates the manufacture of the luminescent display tubes according to this invention.

Demand is growing for luminescent display tubes which are operable at the low voltages which may be supplied by a power source usable for the integrated circuits which drive such tubes. The brightness of the display provided in accordance with this invention enables this demand to be satisfied.

What is claimed is:

1. An anode assembly for a luminescent display tube includes:

a substrate having a plurality of recesses formed in a major surface of said substrate, each of said recesses having a bottom surface and a peripheral wall surface; plurality of anode structures, each of said anode structures being disposed in one of said recesses, each of said anode structures including a layer of electrically conductive material disposed on said bottom surface of said one recess, at least one projecting member of electroconductive material which projecting member is contiguous with and extends outwardly from said electrically conductive layer, and a layer of luminescent material covering said electrically conductive layer and said at least one projecting member.

2. An anode assembly as claimed in claim 1 wherein said at least one projecting member of said anode structure is composed of the same material as said layer of electroconductive material.

3. An anode assembly as claimed in claim 1 wherein said at least one projecting member of said anode structure is in contact with said peripheral wall surface of said one recess.

4. An anode assembly as claimed in claim 1 including a first and a second projecting member, the first of said projecting members being in contact with a first area of said peripheral wall surface of said one recess and the second of said projecting members being in contact with a second area of said peripheral wall surface of said recess which second area is substantially opposed to said first area.

5. An anode assembly as claimed in claim 4 including a third projecting member arranged between said first and said second areas of said peripheral wall surface.

6. An anode assembly as claimed in claim 1 in which at least some of the recesses in said major surface of said substrate are elongated recesses having two elongated opposed side surfaces and in which said anode structures which are disposed in said elongated recesses include a first and a second projecting member, one of said projecting members being in contact with each of said elongated opposed side surfaces.

7. An anode assembly as claimed in claim 6 in which said projecting members cover substantially the entire areas of each of said elongated opposed side surfaces.

8. An anode assembly as claimed in claim 6 including at least one additional projecting member, said additional projecting member being disposed between said elongated opposed walls.

9. An anode assembly as claimed in claim 8 in which said additional projecting member is approximately equally spaced from each of said opposed walls. 

1. An anode assembly for a luminescent display tube includes: a substrate having a plurality of recesses formed in a major surface of said substrate, each of said recesses having a bottom surface and a peripheral wall surface; a plurality of anode structures, each of said anode structures being disposed in one of said recesses, each of said anode structures including a layer of electrically conductive material disposed on said bottom surface of said one recess, at least one projecting member of electroconductive material which projecting member is contiguous with and extends outwardly from said electrically conductive layer, and a layer of luminescent material covering said electrically conductive layer and said at least one projecting member.
 2. An anode assembly as claimed in claim 1 wherein said at least one projecting member of said anode structure is composed of the same material as said layer of electroconductive material.
 3. An anode aSsembly as claimed in claim 1 wherein said at least one projecting member of said anode structure is in contact with said peripheral wall surface of said one recess.
 4. An anode assembly as claimed in claim 1 including a first and a second projecting member, the first of said projecting members being in contact with a first area of said peripheral wall surface of said one recess and the second of said projecting members being in contact with a second area of said peripheral wall surface of said recess which second area is substantially opposed to said first area.
 5. An anode assembly as claimed in claim 4 including a third projecting member arranged between said first and said second areas of said peripheral wall surface.
 6. An anode assembly as claimed in claim 1 in which at least some of the recesses in said major surface of said substrate are elongated recesses having two elongated opposed side surfaces and in which said anode structures which are disposed in said elongated recesses include a first and a second projecting member, one of said projecting members being in contact with each of said elongated opposed side surfaces.
 7. An anode assembly as claimed in claim 6 in which said projecting members cover substantially the entire areas of each of said elongated opposed side surfaces.
 8. An anode assembly as claimed in claim 6 including at least one additional projecting member, said additional projecting member being disposed between said elongated opposed walls.
 9. An anode assembly as claimed in claim 8 in which said additional projecting member is approximately equally spaced from each of said opposed walls. 